128 NEW YORK STATE MUSEUM 



Potsdam and the Pamelia formation (upper Stones River) in the 

 Thousand Island region.^ The formation as defined is thin, not 

 over 60 feet, seemed a unit and was thought tO' be entirely older 

 than the Beekmantown. In its lower portion a variety of L i n g u - 

 1 e p i s acuminata is abundant, while the higher beds contain 

 cystid plates and a large, flat gastropod. These now prove to be 

 identical with the cystid plates and the Pleurotomaria hun- 

 ter ens is (Cleland) which are found in the Tribes Hill lime- 

 stone of the Mohawk valley, whence it follows that the upper por- 

 tion of the Theresa formation in Jefferson county is of lower Beek- 

 mantown age. We are, however, of the opinion that the lower 

 portion is properly to be classed with the Potsdam beneath as of 

 Saratogan (Ozarkic) age and that there are two formations pres- 

 ent instead of one. We also think that an unconformity will be 

 found between the two, now that it is suspected, so that search 

 can be made for it. It is, therefore, unfortunate that a name was 

 given to the supposedly single formation. We suggest, however, 

 the retention of the name Theresa as a designation for the passage 

 beds which occur everywhere in New York between the Potsdam 

 and the overlying Little Falls dolomite, since they have a char- 

 acteristic lithology of their own, and should be and can be mapped 

 separately. 



Correlation of the foregoing sections 



In order to bring out more clearly and concisely our ideas in re- 

 gard to the sections, they are given in generalized form in the ac- 

 companying table. The Little Falls dolomite occurs in all and in 

 fairly uniform thickness except at the extreme west where it is 

 thinned by overlap on the Precambric. The Tribes Hill limestone 

 overlies it in most sections, but thins westward to disappearance 

 in the Mohawk valley; the Saratoga region seems to have been just 

 beyond the reach of its deposits. Correlating the Tribes Hill 

 with the typical dove limestone of division B of the Champlain 

 Calciferous, then sedimentation would seem to have been only 

 locally interrupted in that trough as noted in the vicinity of Ticon- 

 deroga.' But, if the former is older than the latter, as is indicated 

 by faunal evidence, then the whole of the Champlain valley was 

 emerged while the Tribes Hill was being deposited in the Mohawk: 

 valley. 



The Tribes Hill and Little Falls formations seem everywhere 

 unconformable in New York, and we make this unconformity the 



^ Geol. Soc. Am. Bui. 19: 155-76. 



